Conveyors are well known devices and come in many forms. Generally speaking, most common conveyors typically feature a conveyor body (frame), spaced apart pulleys, a conveyor belt that is stretched between the pulleys, and a conveyor belt tracking mechanism for adjusting both belt tension and the tracking of the moving conveyor belt. The tracking of a conveyor belt on the conveyor pulleys may depend largely on how squarely the belt is cut by the belt manufacturer. However, without a tracking mechanism, a conveyor belt will typically track to the left or to the right over time, and will frequently rub against the conveyor body. This rubbing often leads to conveyor noise, conveyor belt wear, and eventually to conveyor belt failure through mechanical abrasion.
Like conveyors themselves, conveyor belt tracking mechanisms are well known in the conveyor industry. While known conveyor belt tracking mechanisms may vary somewhat in design, such mechanisms typically include a tensioning screw located along each side of the conveyor body in the area of an adjustable conveyor drive pulley (see FIG. 1). The drive pulley commonly features at least a slightly trapezoidal or circular crown (profile) to facilitate movement of the conveyor belt along the pulley surface when appropriate.
As best illustrated in FIGS. 2A-2B, turning one of the adjusting screws shown in FIG. 1 results in a canting of the drive pulley with respect to the conveyor frame and the other pulley, and will cause greater tension along one side of the belt. As can be understood from observation of FIGS. 2A-2B, the conveyor belt will move away from the end of the pulley that is placing the belt under the most tension (i.e., the belt moves downward with respect to the drawing page in FIG. 2A and upward with respect to the drawing page in FIG. 2B). Hence, a manipulation of the adjusting screws may be employed to move the belt from one side of the conveyor to the other.
One negative effect of conveyor belt tracking mechanisms that utilize two screws for belt tracking adjustment is that both screws must normally be manipulated to achieve acceptable tracking of the conveyor belt. This operation can be tedious particular but not only because the tracking sensitivity of the belt is often quite high, meaning that even a minute rotation (e.g., ⅛ of one turn, depending on the tread pitch of the screw) of one of the tracking adjustment screws in one direction or the other will lead to the belt shifting away from the centerline of the conveyor.
Also, an unintended consequence of a conveyor belt tracking mechanism like that depicted in FIGS. 1 and 2A-2B is that the use of two adjusting screws during a belt tracking adjustment process often leads to an over-tensioning of the conveyor belt, which may result in an overloading of the pulley bearings and early bearing failure. Such over-tensioning of the conveyor belt is most often associated with conveyor belts comprised of a polyester carcass because the polyester material significantly restricts stretching of the conveyor belt. The benefit of such a conveyor belt is that through increased belt tension, it is possible to prevent the belt from slipping on the drive pulley when a heavy load is carried by the conveyor.
Not all conveyors employ polyester carcass conveyor belts. For example, polyester carcass conveyor belts are prohibited from use in food applications because an accumulation of food debris may remain in the carcass even after a sanitary wash down, and such an accumulation of food debris may lead to food contamination. Consequently, conveyor manufacturers often utilize closed cell stretch belts in food applications. Conveyor belts of such a construction have the benefit of not absorbing food debris or fluids and can be sanitized on the conveyor or removed from the conveyor and sanitized in a separate and typically chlorine-based cleaning solution before being placed back onto the also cleaned conveyor body.
In the case of a conveyor having a closed cell stretch conveyor belt, belt tension on the pulleys is defined by a stretch factor specified by the belt manufacturer. Because of the more stretchable nature of such a conveyor belt, placing additional tension on the belt will not produce a significant tracking improvement because the stretched belt will only add marginal additional tension to the conveyor drive system. Furthermore stretching the conveyor belt to achieve better belt tracking may lead to an increase in the physical length of the conveyor, which may ultimately result in an interference with other conveyors adjacent to the conveyor whose belt has been stretched. Therefore, rather than achieving increased belt traction through belt stretching, increased belt traction on the drive pulley of such a conveyor is more often produced by placing easy to clean grooves over the length of the pulley surface. The grooves act to provide additional traction between the belt and the pulley while still permitting the pulley to be cleaned in a sanitary manner.
In sanitary applications, such as food applications, the use of conveyor belt tracking mechanism adjusting screws with exposed threads is also unacceptable because of the difficulty associated with cleaning out the threads of the screws during conveyor sanitation. Consequently, there is an interest in altogether eliminating conveyor belt tracking mechanism adjusting screws.
An alternative conveyor design having this goal in mind is schematically represented in FIG. 3. In the conveyor of FIG. 3 both the drive and idler pulleys of the conveyor are crowned, with the intent being to keep the conveyor belt from tracking away from the center of the pulleys and conveyor body. A downside to this design, however, is that the conveyor belt will tend to be pushed by both pulleys towards the center of the conveyor, which ultimately leads to a crease in the belt and to early belt failure. Furthermore, the variability of the belt splicing process employed during conveyor belt manufacturing frequently results in an improper tracking of the belt on the conveyor if no other tracking adjustment is provided.
It can be understood from the foregoing background description that there is a need for a conveyor belt tracking mechanism that overcomes the deficiencies of known tracking mechanisms, and for a conveyor employing such a conveyor belt tracking mechanism. Therefore, an objective of the exemplary conveyor belt tracking mechanism embodiments described herein is to overcome the deficiencies of known tracking mechanisms.